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What causes a floating neutral, When the neutral from a transformer, UPS or inverter does not have a neutral earth bond.
Examples of where you will find floating neutrals under normal operation conditions.
Transformers, where one of the secondary output terminals are not grounded.
low voltage control circuits.
Safety supplies.
Mobile Inverters.
Mobile Generators.
Mobile UPS.
Is it dangerous to have a floating neutral, that's the part that requires more discussion. Why, because in some cases it is important that the secondary side is not grounded, a pool safety transformer is a good example. It is regarded an isolated safety supply.
Should the output form a generator be grounded, if used as a mobile device, no. It it is connected to a fixed installation, yes.
Then we move onto the one that has many people very confused, the inverter.
Should the output of an inverter be grounded/bonded to earth, while operating under "normal" conditions, no, so why not, because the inverter uses the bond from the grid supply and therefore the ELU would function correctly and everyone would be happy. IF you bonded the earth/neutral while operating under "normal" conditions, it would create a second bond in the electrical installation (which is not allowed by law) and trip the ELU.
A standard mobile generator which in most cases would be a V-O-V (110-0-110 typical design for the USA), would have a floating neutral. However all the smart people in SA have decided that it is dangerous, so now they are saying the neutral (one terminal) output has to be grounded. The way I see it, the frame of the mobile generator could now end up with 230 volts to the frame, hence the reason for the V-O-V to make it safer 110 VAC.
By connecting the generator to a fixed installation, you would need to install a spike, bond the frame and created a bonded neutral/earth (so that it is no longer a floating neutral) at no point should generator be connected directly to the grid supply, hence the manual or auto changeover, unless it is designed for that application( to blend with the grid supply).
Then we move onto inline UPS systems which function online permanently (they dont switch over) they feed a clean pure sine wave to the supply, most commonly found in IT applications where a good clean stable power supply is required. As technology evolves, more device require a constant clean supply. So we fit all sorts of devices to attempt to reduce the failure of expensive electronic equipment now even in our homes.
Then you will find cheaper UPS devices, which in some cases have a very fast switching time so you would even notice because the computer would stay on. These mobile UPS units have a floating neutral. How would you know, by simply testing L-E and N-E, you will notice what seems like strange voltages between 80 and 120 VAC.
In the past a UPS would supply dedicated socket outlets (red sockets) which would not require earth leakage protection, so there was no need for earth/neutral bonding. We even had a dedicated earth stud for a "clean" earth which has since been scrapped.
Examples of where you will find floating neutrals under normal operation conditions.
Transformers, where one of the secondary output terminals are not grounded.
low voltage control circuits.
Safety supplies.
Mobile Inverters.
Mobile Generators.
Mobile UPS.
Is it dangerous to have a floating neutral, that's the part that requires more discussion. Why, because in some cases it is important that the secondary side is not grounded, a pool safety transformer is a good example. It is regarded an isolated safety supply.
Should the output form a generator be grounded, if used as a mobile device, no. It it is connected to a fixed installation, yes.
Then we move onto the one that has many people very confused, the inverter.
Should the output of an inverter be grounded/bonded to earth, while operating under "normal" conditions, no, so why not, because the inverter uses the bond from the grid supply and therefore the ELU would function correctly and everyone would be happy. IF you bonded the earth/neutral while operating under "normal" conditions, it would create a second bond in the electrical installation (which is not allowed by law) and trip the ELU.
A standard mobile generator which in most cases would be a V-O-V (110-0-110 typical design for the USA), would have a floating neutral. However all the smart people in SA have decided that it is dangerous, so now they are saying the neutral (one terminal) output has to be grounded. The way I see it, the frame of the mobile generator could now end up with 230 volts to the frame, hence the reason for the V-O-V to make it safer 110 VAC.
By connecting the generator to a fixed installation, you would need to install a spike, bond the frame and created a bonded neutral/earth (so that it is no longer a floating neutral) at no point should generator be connected directly to the grid supply, hence the manual or auto changeover, unless it is designed for that application( to blend with the grid supply).
Then we move onto inline UPS systems which function online permanently (they dont switch over) they feed a clean pure sine wave to the supply, most commonly found in IT applications where a good clean stable power supply is required. As technology evolves, more device require a constant clean supply. So we fit all sorts of devices to attempt to reduce the failure of expensive electronic equipment now even in our homes.
Then you will find cheaper UPS devices, which in some cases have a very fast switching time so you would even notice because the computer would stay on. These mobile UPS units have a floating neutral. How would you know, by simply testing L-E and N-E, you will notice what seems like strange voltages between 80 and 120 VAC.
In the past a UPS would supply dedicated socket outlets (red sockets) which would not require earth leakage protection, so there was no need for earth/neutral bonding. We even had a dedicated earth stud for a "clean" earth which has since been scrapped.
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